1. Field of the Invention
The present invention relates to a diaphragm carburetor wherein the temperature of the carburetor is lowered to reduce the occurrence of bubbles in the fuel.
2. Description of the Related Art
When bubbles occur in the fuel in the engine carburetor of a hand-held mower, hand-held trimmer, or the like, the rotation of the engine fluctuates, impeding work. Bubbles occur primarily when the temperature inside the carburetor is increased by various types of heat from the engine.
Usually, the carburetor unit is heated by heat generated by the engine when the engine is operated continuously, and the carburetor is cooled by the heat of vaporization of the fuel. The temperature of the carburetor is balanced by this simultaneous heating and cooling, and the carburetor is designed so that bubbles do not form in the fuel inside the carburetor in such a state.
However, as output has increased and fuel consumption decreased in modern low-emission engines, the amount of heat generated by the engine has increased. Despite this, the amount of cooling of the carburetor by the heat of vaporization has decreased, the temperature of the carburetor during operation has the tendency to increase gradually, and problems due to bubbles have become more prone to occur.
In a conventional fuel supply device for a floatless carburetor, the difference in temperature is reduced between the carburetor mounted to the engine and the fuel supplied from the fuel tank to the carburetor, and evaporation of the fuel in the carburetor is suppressed (see Japanese Patent No. 4007703).
In this publicly known technique, the fuel drawn from the fuel tank by the fuel pump passes through a fuel supply channel. In the process, the fuel passes through a fuel relay chamber that is formed integrally with an insulator, and since the insulator is somewhat heated by conduction of heat from the engine during prolonged operation of the engine, the fuel passing through the fuel relay chamber is also appropriately heated. Consequently, it is possible to reduce the difference in temperature between the fuel drawn out of the fuel relay chamber by the fuel pump of the carburetor and the carburetor that is heated to a relatively high temperature by the engine heat. As a result, sudden temperature changes of the fuel inside the carburetor can be prevented and evaporation of the fuel can be suppressed.